A Fully Symmetrical Quantum Key Distribution System Capable of Preparing and Measuring Quantum States

We propose a fully symmetrical QKD system that enables quantum states to be prepared and measured simultaneously without compromising system performance. Over a 25.6 km fiber channel, we demonstrate point-to-point QKD operations with asymmetric Mach–Zehnder interferometer modules. Two interference visibilities of above 99% indicate that the proposed system has excellent stability. Consequently, the scheme not only improves the feasibility of distributing secret keys, but also enables QKD closer to more practical applications.